1. Field of the Invention
The present invention relates to product ejectors for use in injection molding machines and, particularly, to a product ejector in a direct-acting type mold clamping system in which a ball screw is driven by a servomotor to move a moving platen fixedly mounted to a ball nut threadedly engaged with the ball screw, thereby carrying out mold clamping.
2. Description of the Art
In an injection molding machine, there is known a product ejector for removing a product from a mold, which is of such a type that, during rearward movement of a moving platen toward a rear platen, a rod fixed to the rear platen pushes an ejector plate, short of a point of time mold opening is completed, to project a product ejector bar fixedly mounted to the ejector plate, toward the mold mounted on the moving platen, thereby ejecting a product from the mold. A product ejector is also known, which is of such a type that a driving source separate from a driving source for a mold clamping system is employed to drive a product ejector bar to project the same, thereby removing a product from a mold.
A direct-acting type mold clamping system also has been developed, in which a ball screw is rotated by a servomotor, to move a moving platen which is movable together with a ball nut threadedly engaged with the ball screw, to thereby carry out mold closing, mold clamping and mold opening.
It is required for the above direct-acting type mold clamping system to set a length of the ball screw supported by a rear platen, to a considerably large value corresponding to a moving stroke of the moving platen. It is also required to prevent the ball screw and the platen from interfering with each other at a position where mold opening is completed. As a result, the spacing distance between the rear platen and the moving platen becomes long. Accordingly, if the rod for pushing the product ejector bar mounted on the side of the moving platen is fixed to the rear platen, the rod becomes long, so that deflection might occur or a problem might arise as to strength. On the other hand, if an attempt is made to carry out driving of the product ejector bar without the use of the long rod, a driving source for ejection of a product is especially required, making the injection molding machine expensive.